1. Field of the Invention
The present invention relates to a resolver, and more particularly, a resolver having a structure in which a fault can be rapidly detected even when windings are short-circuited. Furthermore, the present invention relates to a method for detecting a fault by means of provision of a fault detection circuit for detecting such an accident.
2. Description of the Related Art
A resolver is one kind of synchronous transmitter which provides from its output windings an output signal that has an amplitude modulated in accordance with X and Y components of a rotation angle of its rotor. Conventionally, the resolver is typically used as a detection system or for triangulation calculation in a servomechanism.
For example, a resolver as shown in FIG. 14 includes a rotor, a stator and two pairs of orthogonal windings, i.e., excitation windings 111 and output windings 112. Two of such resolvers make a pair, in which the stators or rotors of the respective resolvers are coupled to each other. One phase of either the stator or the rotor of the resolver functioning as a transmitter is excited by AC power. Thus, an AC output in accordance with a difference between a rotation position of the transmitter resolver and that of the receiver resolver can be obtained at the corresponding orthogonal phase of the transmitter resolver.
An alternative structure of the resolver is known as a variable reluctance resolver. In this structure, a rotor has a shape of a rectangle or the like and no winding is provided around the rotor. A stator is provided with a plurality of poles with an excitation winding and an output winding being wound around the same pole of the stator. A sum of outputs from the plurality of output windings at the different poles is provided as a single output from the output windings.
FIG. 16 shows an example of the winding structure of the above-mentioned resolver. The relationship between the excitation winding 111 and the output winding 112 to be wound around any one of the poles is defined as follows. The respective excitation windings 111 are wound around the poles so that an N pole and an S pole of the resultant magnetization appear alternatively at the adjacent poles, while the respective output windings 112 are wound around the poles so that an N pole and an S pole of the resultant magnetization appear alternatively at every two poles. More specifically, when the excitation winding 111 at the first pole provides an N pole, N poles are generated by the output windings 112 at the first and second poles, while S poles are generated by the output windings 112 at the third and fourth poles, and such a configuration will appear in the repeated manner.
In the resolver having the above-mentioned construction, a fault such as short-circuit between the windings may occur. Thus, fault detection is necessary for improving the reliability of an apparatus incorporating therein a resolver.
FIG. 15 shows an example of a conventional resolver and a fault detection circuit utilizing the same. The configuration in FIG. 15 includes a resolver 10 and a resolver fault detection circuit 11. The resolver 10 has output windings 112X and 112Y for respectively outputting an X direction component and a Y direction component of a rotor of a resolver 10. The resolver fault detection circuit 11 includes square calculators 121X and 121Y respectively connected to the output windings 112X and 112Y, an adder 123 for calculating a sum of outputs from both of the square calculators 121X and 121Y, a rectifier circuit 124 for rectifying an output VE from the adder 123, and a comparator circuit 125 for comparing an output from the rectifier circuit 124 with a reference voltage.
In order to facilitate understandings of the invention, the variable reluctance resolver is taken as an example which has a structure in which a stator is provided with a plurality of poles. The same pole of the stator is provided with an excitation winding 111, an output winding 112X for outputting an X direction component of a rotor, and an output winding 112Y for outputting a Y direction component of the rotor, that are wound therearound. A sum of outputs of the output windings wound around the respective poles is provided as a single output from the output windings. With respect to such a variable reluctance resolver, the relationship of phases among the excitation winding 111 and the output windings 112X and 112Y for respectively outputting the X direction component and the Y direction component of the rotor will be described with reference to FIG. 16.
In the case where the direction of magnetization generated by a voltage induced by the excitation winding 111 in the output winding 112X for outputting the X direction component of the rotor is the same as the direction of magnetization of the excitation winding 111, a voltage ENS induced at any one of the poles can be expressed by Equation 1 when an AC voltage VP as expressed in E sin xcfx89t is applied to the excitation winding 111, where xcfx89 represents an angular frequency which is expressed as 2xcfx80f, f represents a frequency, a and b are constants defined by characteristics of the excitation winding 111, the output winding 112X, the rotor and the stator.
ENS=(a+b sin xcex8)xc2x7E sin xcfx89txe2x80x83xe2x80x83(Eq. 1)
On the other hand, in the case where the direction of magnetization generated by the voltage induced by the excitation winding 111 in the output winding 112X is different from the direction of magnetization of the excitation winding 111, a voltage ENN induced at any one of the poles can be expressed by Equation 2.
ENN=(xe2x88x92a+b sin xcex8)xc2x7E sin xcfx89txe2x80x83xe2x80x83(Eq. 2)
The relationship between the excitation winding and the output winding to be wound around any one of the poles is defined as illustrated in FIG. 16. In the case where the windings wound around the first pole and the second pole in such a structure are connected in series, the resultant voltage V12 can be expressed by Equation 3 below in view of the above-mentioned Equations 1 and 2.
V12=(a+b sin xcex8)xc2x7E sin xcfx89t+(xe2x88x92a+b sin xcex8)xc2x7E sin xcfx89txe2x80x83xe2x80x83(Eq. 3)
Similarly, a voltage V34 expressed in Equation 4 is generated by the third and fourth poles.
V34=(xe2x88x92a+b sin xcex8)xc2x7E sin xcfx89t+(a+b sin xcex8)xc2x7E sin xcfx89txe2x80x83xe2x80x83(Eq. 4)
From Equations 3 and 4, the terms with the constant a are eliminated in the case where the adjacent poles are connected in series, so that voltages V12 and V34 as expressed in Equation 5 can be obtained.
V12=2b sin xcex8xc2x7E sin xcfx89t=V34xe2x80x83xe2x80x83(Eq. 5)
Accordingly, when the output windings of all of the poles are connected in series in the case where the number of the poles is a multiple of 2, the terms with the constant a are eliminated so that an output voltage VS from the output winding 112X can be expressed by Equation 6.
VS=K sin xcex8xc2x7E sin xcfx89txe2x80x83xe2x80x83(Eq. 6)
In the equation, K is a constant defined in accordance with the constant b and the number of poles, and is expressed by Equation 7 where N represents the number of poles.
K=Nxc2x7Bxe2x80x83xe2x80x83(Eq. 7)
Similarly, an output from the output winding 112Y for outputting the Y direction component of the rotor can be expressed by Equation 8, since the output winding 112Y is wound around so that the phase thereof is shifted by 90xc2x0 with respect to the rotor.
VC=K cos xcex8xc2x7E sin xcfx89txe2x80x83xe2x80x83(Eq. 8)
When output voltages from the above-mentioned resolver are applied to the square calculators 121X and 121Y in FIG. 15, the square calculators 121X and 121Y respectively provide voltage outputs as expressed in Equations 9 and 10.
VSX=VS2=K2xc2x7sin xcex82xc2x7E2 sin2 xcfx89txe2x80x83xe2x80x83(Eq. 9)
VCY=VC2=K2xc2x7cos xcex82xc2x7E2 sin2 xcfx89txe2x80x83xe2x80x83(Eq. 10)
Accordingly, an output VE of the adder 123 obtained by summing up the outputs of the square calculators 121X and 121Y can be expressed as Equation 11.
VE=K2xc2x7E2 sin2 xcfx89txc2x7(sin2 xcex8+cos2 xcex8)xe2x80x83xe2x80x83(Eq. 11)
When the excitation winding 111 and the output windings 112X and 112Y for respectively outputting the X direction component and the Y direction component of the rotor operate normally, the term (sin2 xcex8+cos2 xcex8) is always 1. Accordingly, the output VE always has a constant value as expressed in Equation 12 irrespective of the value of rotation angle xcex8.
VE=K2xc2x7E2 sin2 xcfx89txe2x80x83xe2x80x83(Eq. 12)
However, even when the resolver operates normally, the value of sin2 xcex8 becomes 0 when the rotation angle xcex8 is 0xc2x0, resulting in the output from the output winding 112X for outputting the X direction component of the rotor being zero. On the other hand, if the output winding 112X is short-circuited, the output voltage from the output winding 112X also becomes zero. Accordingly, it cannot be recognized whether the output becomes zero because the rotation angle xcex8 of the output winding 112X is 0xc2x0 or because the output winding 112X is short-circuited.
Similarly, even when the resolver operates normally, the value of cos2 xcex8 becomes 0 when the rotation angle xcex8 is 90xc2x0, resulting in the output voltage from the output winding 112Y for outputting the Y direction component of the rotor being zero. On the other hand, if the output winding 112Y is short-circuited, the output voltage from the output winding 112Y also becomes zero. Accordingly, it cannot be recognized whether the output voltage becomes zero because the rotation angle xcex8 of the output winding 112Y is 90xc2x0 or because the output winding 112Y is short-circuited.
As set forth above, in the conventional variable reluctance resolver, there is no output terminal provided at the middle point in each of the output windings 112X and 112Y. Accordingly, only the voltage across the opposite output terminals of the output winding 112X and the voltage across the opposite output terminals of the output winding 112Y are obtained. The fault detection circuit is also configured to detect a fault by means of the sum of squared values of the respective output voltages using the above voltage.
Since the sum of the squared values of the output voltages across the output windings 112X and 112Y is used as a detection signal, a constant output voltage can be always obtained when the resolver operates normally, while the value thereof changes when a fault occurs, thereby realizing a fault detection. However, even when the resolver operates normally, the value of sin2 xcex8 becomes 0 with the rotation angle xcex8 being 0xc2x0 so that the output voltage from the output winding 112X becomes 0.
On the other hand, the output voltage from the output winding 112X also becomes 0 when the output winding 112X is short-circuited. Accordingly, the conventional structure has a disadvantage in which it cannot be recognized whether the output becomes zero because the rotation angle xcex8 of the output winding 112X is 0xc2x0 or because the output winding 112X is short-circuited.
Similarly, even when the resolver operates normally, the value of cos2 xcex8 becomes 0 with the rotation angle xcex8 being 90xc2x0 so that the output voltage from the output winding 112Y which outputs the Y direction component of the rotor becomes 0. On the other hand, the output voltage from the output winding 112Y also becomes 0 when the output winding 112Y is short-circuited. Accordingly, the conventional structure has a disadvantage in which it cannot be recognized whether the output becomes zero because the rotation angle xcex8 of the output winding 112Y is 90xc2x0 or because the output winding 112Y is short-circuited.
As set forth above, the conventional resolver cannot detect a fault at a specific rotation angle of a rotor when an accident is resulted from short-circuiting, and therefore, the fault detection is not operated accurately. Furthermore, since a difference between an amplitude when a fault occurs and an amplitude when a resolver operates normally is detected, a signal-to-noise ratio cannot be set at a large value. In addition, upon the fault detection, a fault in the output winding 112X for outputting the X direction component of the rotor of the resolver and a fault in the output winding 112Y for outputting the Y direction component thereof are not distinguished. Accordingly, it cannot be distinguished whether the fault occurs in the output winding 112X or in the output winding 112Y. This is not appropriate for obtaining data to be used for an accident analysis.
Furthermore, with development of electric vehicles or the like, it has been attempted to replace a power steering device driven by oil-pressure for automobiles or the like with a resolver. However, the conventional resolver is inappropriate to be used in automobiles in which emphasis should be placed upon safety, since it may not be able to determine whether or not a fault occurs even when a fault actually occurs in the resolver.
In order to overcome the above-mentioned disadvantages in the conventional art, the present invention is intended to provide a resolver having a structure in which a fault such as short-circuiting among windings or the like can be easily detected, a fault detection circuit for realizing the above, and a fault detection method utilizing the above circuit. In order to achieve the above-mentioned objective, a resolver in accordance with a first aspect of the present invention comprising a stator, a rotor, an excitation winding and an output winding, characterized in that an output terminal is provided at a middle point between opposite end terminals of the output winding.
Another resolver in accordance with a second aspect of the present invention comprising a stator, a rotor, an excitation winding and an output winding, the excitation winding and the output winding being wound around the identical pole of the stator, characterized in that an output terminal is provided at a middle point between opposite end terminals of the output winding.
In accordance with a third aspect of the present invention, a resolver fault detection circuit to be used for a resolver comprising a stator, a rotor, an excitation winding and an output winding, is provided. The circuit comprises: an output terminal provided at a middle point between opposite end terminals of the output winding; a difference voltage detection circuit for obtaining a difference voltage between a first output voltage, between one of the opposite end terminals of the output winding of the resolver and the middle point, and a second output voltage, between the other one of the opposite end terminals of the output winding and the middle point; and a comparator circuit for outputting a signal as a fault signal when an output voltage from the difference voltage detection circuit deviates from a reference value.
A resolver fault detection method is provided in accordance with a fourth aspect of the present invention so as to be used for a resolver comprising a stator, a rotor, an excitation winding and an output winding, characterized in that the method comprises the step of obtaining a fault detection signal from a resolver fault detection circuit to detect that the resolver is faulty. The resolver fault detection circuit comprises: an output terminal provided at a middle point between opposite end terminals of the output winding; a difference voltage detection circuit for obtaining a difference voltage between a first output voltage, between one of the opposite end terminals of the output winding of the resolver and the middle point, and a second output voltage, between the other one of the opposite end terminals of the output winding and the middle point; and a comparator circuit for outputting a signal as a fault signal when an output voltage from the difference voltage detection circuit deviates from a reference value.
Another resolver fault detection method in accordance with a fifth aspect of the present invention comprises the steps of: obtaining a fault detection signal of a resolver fault detection circuit, the fault detection signal indicating a fault of a first output winding for outputting an X direction component of a rotor; obtaining a fault detection of the resolver fault detection circuit, the second signal indicating a fault of a second output winding for outputting a Y direction component of the rotor; and obtaining a logical sum of the first signal and the second signal as a fault detection signal.
As set forth above, in accordance with the present invention, a resolver comprising a rotor, a stator, an excitation winding and an output winding is configured so that an output terminal is provided at the middle point,-in the output winding. Thus, a difference voltage between a first output voltage, between one end of the output winding and the middle point, and a second output voltage, between the other end of the output winding and the middle point, can be obtained.
When no fault occurs, the first output voltage between one end of the output winding and the middle point has the same value as the second output voltage between the other end of the output winding and the middle point. Accordingly, an output voltage from the difference voltage detection circuit for obtaining a difference between the above-mentioned first and second output voltages becomes zero when no fault occurs in the output winding, while the difference voltage detection circuit outputs a difference voltage when a fault occurs at some point in the output winding.
When a fault occurs in the output winding, the output from the difference voltage detection circuit is shifted from a reference value. The comparator circuit provides an output as a fault signal to indicate that an fault occurs in the resolver. The fault in the output winding can include short-circuiting in the identical output winding, short-circuiting between the different output windings, short-circuiting between the excitation winding and the output winding, or the like. In either case, the difference value voltage comes to have a non-zero value when something extraordinary occurs, thereby functioning to detect a fault. A variable reluctance resolver is applicable to various fields in automobiles including, other than to an electric power steering system, e.g., a hybrid car system, an electric vehicle system, a braking-by-wire system, a suspension-by-wire system, an accelerator-by-wire system, a valve control system, a stator alternator system, or the like. Furthermore, a variable reluctance resolver is also applicable to other fields such as control of various robots, or control of a servomotor.